Hi all.
Watching the Portland Oregon news here, and during the weather segment there was a reference to “waves” and “swells” on the ocean. My Dad asked what the difference between them was. Me, not being the nautical type, replied, “I dunno. Maybe waves are what crashes on the shore, and swells are those water humpy thingys out to sea. I think I’ll post a thread on GQ.”
So here it is. Does anyone know?
From “The American Practical Navigator” (or Bowditch):
Swell: A relativley long wind wave, or series of waves, that has traveled out of the generating area. In contrast the term SEA is applied to the waves while still in the generating area. As these waves travel away from the area in which they are formed, the shorter ones die out. The surviving waves exhibit a more regular and longer period with flatter crests. When these waves reach shoal water, they become more prominent in height and of decreased wave length and are then known as ground swell.
A wave, is simply a ridge above the surface of the liquid. So, in other words, a swell is a type of wave.
Normally the swell is the waves that you see (generally larger and smoother) which are generated elsewhere. The seastate overlies the swell and is caused at that place by the current wind.
Thanks for the replies!
Sounds like the newscaster is using colloquial rather than American Standard English, causing some confusion.
Swells are nattily dressed rich folks. Waves are female members of the US Navy. It’s an obsolete usage now; the Navy calls them something else these days.
If only “flapper” was a nautical term.
It is. The check valve in some head (toilet) pumps is called a flapper.
Ignorance fought! 
Actually, the colloquial use is not far removed from the standard or the technical.
In colloquial usage, waves looks like small or large hills marching across the ocean, one file after the other. Swells look more like the ocean is made of some flexible plastic-like liquid that rises and falls as it is flexed. Swells tend to look smoother than other waves (recognizing that swells are a form of waves), appearing to “swell” up from the sea. The swells that preceed hurricanes are often so broad from front to back that they do not actually break when they reach the shore. (The later wind-driven waves obviously do break.)